Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already flag readOnlyHint=false and idempotentHint=false, but the description adds crucial context: each call is a new entry (non-idempotent), the history is write-only ('no tool reads it back'), and it does not replace persistent storage via other tools. It also clarifies that the history rides along with the user's data export, which is not obvious from annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but every sentence earns its place: purpose, exclusions, idempotency warning, persistence note, return value. It front-loads the core action and then systematically addresses edge cases. No filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a write-only event logger with an output schema and clear annotations, this description covers all decision points: when to call, what types exist, how to format payload, when to omit, repetition risk, and persistence semantics. An agent has everything needed to call it correctly without external lookup.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so parameters are documented, but the description adds real value: it explains the payload's purpose with concrete examples per event type and says when to omit it. It also ties the type enum to the coaching-prompt step, which is more than the schema's generic 'Which milestone happened.' This goes beyond the baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb+resource ('Append a dated milestone to the user's coaching history') and immediately enumerates the exact event types it records. It explicitly names sibling tools (log_session, upsert_goal) to disambiguate, leaving no doubt about what this tool is for.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives explicit timing ('at the end of the step the coaching prompt names'), explicit exclusions ('not for ordinary chat, logged workouts (log_session) or goal edits themselves (upsert_goal)'), and a caution about non-idempotency ('Each call adds a new entry, so do not repeat one'). This is textbook when-to-use guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.